package com.example.lock;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;

public class SemaphoreTest {
    public static void main(String[] args) {
        ExecutorService executorService = Executors.newCachedThreadPool();
        final Semaphore semaphore = new Semaphore(3);
        for (int i = 0; i < 10; i++) {
            Runnable runnable = new Runnable() {
                public void run() {
                    try {
                        semaphore.acquire();
                        System.out.println("线程" + Thread.currentThread().getName() + "进入，当前已有" + (3 - semaphore.availablePermits()) + "个并发");

                        Thread.sleep((long) (Math.random() * 10000));

                        System.out.println("线程" + Thread.currentThread().getName() + "即将离开");
                        semaphore.release();

                        //下面代码有时候执行不准确，因为其没有和上面的代码合成原子单元
                        System.out.println("线程" + Thread.currentThread().getName() + "已离开，当前已有" + (3 - semaphore.availablePermits()) + "个并发");

                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }

                }
            };
            executorService.execute(runnable);
        }
    }
}
